1. Field of the Invention
The invention relates to an assembly for regulating and/or monitoring the electric heating of a catalytic converter located downstream of an internal combustion engine as seen in an exhaust gas flow direction, for detoxifying the exhaust gas. The engine is provided with and controlled by an engine control system.
Electrically heatable catalytic converters are used in motor vehicles in order to meet especially stringent exhaust gas regulations. As a rule, they are disposed upstream of a main converter, as seen in the exhaust gas flow direction.
Excessive amounts of pollutants are produced in internal combustion engines particularly during the so-called cold starting phase, i.e. in the first few minutes of operation, before the engine reaches its final operating temperature. Precisely in this phase, the resultant pollutants cannot be well converted in catalytic converters, because these converters have not reached their operating temperature yet.
2. Description of the Related Art
To remedy this, WO 89/10470 and WO 89/10471 disclose electrically heated converters and methods for operating them. Such converters are heated with a relatively high current within a relatively short time to the temperature necessary for the proper catalytic reactions, so that a considerable portion of the pollutants produced in the cold starting phase can be converted. The heatable converters can be heated to their operating temperature either before the engine is started or immediately after it is started. It has also been known to combine these options. The high energy consumption of electrically heatable converters and the current intensities required for rapidly heating them make such a converter an atypical power consumer in a motor vehicle, which has to be electronically regulated and electrically switched using special means.
Two mutually contradictory interests must be taken into account. On the one hand, to meet exhaust gas regulations, it must be assured that the electrically heatable catalytic converter will reliably perform its task each time the engine is started. On the other hand, the availability of the motor vehicle should not be impaired by this component, as would be conceivable if there were malfunctions in the heatable converter unless additional precautions are taken. The fire safety of a motor vehicle must naturally also be assured, and damage to the exhaust cleaning system itself should be reliably avoided.